Flameproof thermoplastic resin compositions have long been in use, and their continuously increasing demand has promoted research and development efforts in the field. Examples of flame retardant thermoplastic resins are resins of polyesters, polyamides, polyethylenes, polyethylene oxides, acrylonitrile/butadiene/styrene (ABS), polyacetals, polystyrenes, and polycarbonates. Among these resins, polycarbonates, which exhibit a glass transition temperature of as high as 150.degree., high impact and heat resistance, and limited oxygen index(LOI) of up to 25, are widely used for parts of automobiles and electrical appliances owing to their typical flame resistance of UL 94 V2 and high mechanical strength. The impact strength of polycarbonate resins alone, if used as base resin, is sensitively affected by their thickness and notch, however. Considering that a tiny crack on the surface of their molded products seriously deteriorate the impact strength, the use of polycarbonate alone as the base resin is not recommended. It is recommended that other resins be added in order to improve the processability of the polycarbonates. ABS resins, if added to polycarbonates, are known to improve the processability of the polycarbonate resins.
Resins used for housing materials of home appliances and computers must be flame resistant for the sake of fire prevention. Halogen or antimony containing compounds have been used to render flame resistance to thermoplastic resins. These compounds, however, result in the corrosion of the mold itself by the hydrogen halide gases released during the molding process and are fatally harmful due to the toxic gases liberated in the case of fire. As disclosed in European Patent No. 333,694, bromine-substituted phenylphosphates, when used in the preparation of flameproof polycarbonate/ABS resin compositions, enhance the heat resistance, but liberate hydrogen halide gases. The use of polybrominated diphenyl ethers has been prohibited due to the release of toxic gases such as dioxin and difuran during combustion in Germany. Thus, phosphorous compounds have attracted much attention recently because of their good flame resistance in solid phase and little liberation of toxic gases during combustion.
The use of phosphorous compounds to render flame resistance to polycarbonate/ABS resin compositions, as disclosed in Japanese Patent Laid Open No. 62-4717, prevented the dripping of flaming particles during combustion due to the polyfluoroalkyl resins used. This, however, resulted in an unsatisfactory flame resistance and the surface segregation of the flame retarding agent during the molding process, called "juicing", degrading the physical properties of the resin compositions. In order to prevent such a juicing phenomenon, oligomeric phosphate compounds were used in the preparation of polycarbonate/ABS resin compositions to render the flame resistance, as disclosed in European Patent No. 363,608. This improved the heat resistance, but failed to solve the juicing problem completely, and required a complicated mixing apparatus in the extruder because the flame retarding phosphorous compounds were liquid at room temperature.
In this light, the present inventors developed new thermoplastic resin compositions which have a flame resistance of UL 94 VO, good weathering resistance and heat stability, no juicing problem, and improved heat resistance.
An object of the present invention is to provide novel thermoplastic resin compositions with a good flame and weathering resistance, and heat stability, and no juicing problem by adding flame retarding phosphorous compounds and polyfluoroaklyl resins to the resin mixture.
Another object of this invention is to provide flameproof thermoplastic resin compositions with a good processability during molding process.